2. Nervous System

Question 1

2 Parts of the Nervous System

Answer 1

Central nervous system (CNS):

• Consists of the brain and the spinal cord
• Functions as a coordination centre which processes information

Peripheral nervous system (PNS):

• Consists of the nerves and receptors
• The nerves link the receptors to the CNS and the CNS to the effectors

Question 2

Nerve

Definition

Answer 2

A nerve is an organ consisting of a bundle of nerve fibres enclosed in a sheath of connective tissue.

Question 3

Neurone

Structure

Answer 3

A neurone is made up of a cell body (contains nucleus, cytoplasm, and other organelles) and processes known as nerve fibres (dendrons and axons).

Question 4

Nerve Fibres

Types + Functions

Answer 4

There are 2 types of nerve fibres:

Dendrons transmit nerve impulses to the cell body.

• The end branches of dendrons are called dendrites which receive signals from other neurones or receptors.

Axons transmit nerve impulses away from the cell body.

• The ends of the axons are called axon terminals which transmit nerve impulses to other neurones or effectors.

Question 5

Myelin Sheath

Structure + Function

Answer 5

Structure:

• An insulating layer around nerves fibres made up of protein and lipids.

Function:

• The presence of myelin sheath insulates nerve fibres to increase the speed of transmission of nerve impulses.

Question 6

Nodes of Ranvier

What they are

Answer 6

Nodes of Ranvier are regions on nerve fibres where myelin sheath is absent.

Question 7

Synapse

What it is

Answer 7

A synapse is the gap or junction between two neurones or between a neurone and effector (muscle or gland).

Question 8

What happens when the nerve impulse reaches the axon terminals?

Process

Answer 8

1. When the nerve impulses reach the axon terminals, a chemical, neurotransmitter, is released into the synapse, which alters the activity of the receiving cells.
2. Upon release of the neurotransmitter, depending on where a neurone terminates, it can cause a muscle cell to contract, a gland cell to secrete or another neurone to transmit a nerve impulse.

Question 9

Sensory Neurone

Structure + Function

Answer 9

Structure:

• Circular cell body
• Long dendron and short axon
• The cell body and dendron are outside the CNS and the axon is inside the CNS

Function:

• Transmit nerve impulses from receptors to the CNS

Question 10

Relay Neurone

Structure + Function

Answer 10

Structure:

• Irregular or circular cell body
• Whole neurone is found inside the CNS

Function:

• Transmit nerve impulses from sensory neurones to motor neurones
• Trasmit nerve impulses to other relay neurones in the CNS

Question 11

Motor Neurone

Structure + Function

Answer 11

Structure:

• Irregluar cell body
• Has dendrites and long axon
• The cell body and dendrites are in the CNS and the axon is outside the CNS

Function:

• Transmit nerve impulses from the CNS to the effectors

Question 12

Function of Nervous System

Answer 12

The brain, spinal cord, and nerves serve to coordinate and regulate bodily functions by helping organisms adjust rapidly to any changes in their environment and enable various parts of the body to coordinate with each other.

Question 13

Reflex

Definition

Answer 13

A reflex is any immediate response to a specific stimulus that occurs without any conscious effort (automatic).

Question 14

Difference between simple reflexes and conditioned reflexes

Answer 14

Simple reflexes are built-in, unlearned responses, and they have protective functions.
Conditioned reflexes are acquired from past experiences of learning with a stimulus which was originally not effective in producing the response.

Question 15

Types of Simple Reflexes

Answer 15

Spinal reflex action:

• The reflex centre is in the spinal cord
• Examples: withdrawal reflex and knee jerk reflex

Cranial reflex action:

• The reflex centre is in the brain
• Examples: blink reflex, pupil reflex and tearing reflex

Question 16

Reflex Arc

Definition

Answer 16

A reflex arc is the neural pathway in accomplishing a reflex activity, which is the shortest pathway by which impulses travel from the receptor to the effector.

Question 17

Describe a general reflex arc

Answer 17

1. When a stimulus stimulates the receptor, nerve impulses are generated.
2. Nerve impulses travel along the sensory neurone to the (brain/spinal cord), which is the reflex centre.
3. In the (brain/spinal cord), neurotransmitters are released across the synapse between the sensory neurone and relay neurone.
4. Nerve impulses travel along the relay neurone and neurotransmitters are released across another synapse between the relay neurone and the motor neurone.
5. Nerve impluses leave the (brain/spinal cord) along the motor neurone to the effector. The (name of effector) is the effector which response.